1. Field of the Invention
The present invention relates to a dielectric resonance oscillation circuit using a microstrip line, a dielectric resonator and a transistor.
2. Description of the Background Art
In a receiving converter for satellite broadcasting employing Ku-band, a local oscillation signal of extremely high frequency of 10 GHz to 12 GHz has been utilized. Correspondingly, it has become common for a local oscillation circuit to employ a field effect transistor (FET) having a high cutoff frequency (Ft).
FIG. 4 illustrates a pattern and parts arrangement of a dielectric resonance oscillation circuit utilizing such a FET. Specifically, a microstrip line 52 has one end connected to a gate terminal 58 of FET 51 and the other end grounded via a terminating resistance 53 of 50xcexa9. A dielectric resonator 4 is provided at an appropriate distance maintained from microstrip line 52 within a range where it can be coupled with microstrip line 52 at high frequency. With such an arrangement, a change in location of dielectric resonator 4 is accompanied by a change in impedance of dielectric resonator 4 as seen from gate terminal 58.
The oscillation circuit above comes to operate for oscillation when the impedance of dielectric resonator 4 as seen from a source terminal 59 of FET 51 exhibits characteristics of negative resistance. As dielectric resonator 4 is moved in parallel with microstrip line 52, at the time when it arrives at a specific position, the impedance of dielectric resonator 4 seen from source terminal 59 attains such characteristics of negative resistance. Thus, by properly positioning the dielectric resonator 4, a stable oscillating operation is ensured. A signal generated by such an oscillating operation is output from source terminal 59. The oscillation signal is then externally taken out from an oscillation signal output terminal 57, via a stub 55 for output matching and a capacitor 56 for removal of a direct-current (DC) component. In FIG. 4, 60 denotes a DC supply terminal.
The characteristics of negative resistance as described above exhibit periodicity in that they appear every time dielectric resonator 4 moves a distance equal to a wavelength of the oscillation frequency. If dielectric resonator 4 is placed close to FET 51, the loops of the electric field generated from dielectric resonator 4 strongly affect FET 51, thereby increasing phase noise. Thus, dielectric resonator 4 is placed as far as possible from FET 51 within a range allowed by a size of an enclosure containing the oscillation circuit.
Currently, however, there is a pressing demand for increasing an amount of transmissible data for the Internet, for two-way communications, and in the fields where multi-channel and/or high-definition broadcasting is pursued, e.g., for digital broadcasting by broadcast-satellite (BS) that has recently been introduced to Japan. To meet such a demand, there is a growing tendency to employ 8-value PSK (phase shift keying) as a modulation technique, instead of 4-value PSK.
When such transition from 4-value PSK to 8-value PSK takes place, however, a permissible level of phase rotation in a signal transmission path becomes small. Accordingly, in the specification of a block handling a signal of high frequency, a permissible level of phase noise is set to a small value.
More specifically, in the phase shift keyed modulation techniques, data are identified by phase distribution on a complex plane. Thus, tolerance for phase variation for the 8-value PSK becomes much narrower than that for the 4-value PSK. When performing frequency conversion in the block handling a signal of high frequency, a local oscillation signal is required. Such a local oscillation signal includes undesired phase noise, which causes deviation of the phase distribution of the modulated signal being transmitted. Accordingly, for the frequency conversion of a signal by the 8-value PSK, a signal of low phase noise should be used as the local oscillation signal.
If FET 51 is being used as an oscillation element, it is difficult to decrease the phase noise, since undesired phase noise included in the oscillation signal tends to increase. Thus, a technique has been proposed which employs PLL (phase locked loop) to decrease such undesired phase noise. In order to use this technique, however, a reference signal oscillation circuit employing a temperature compensated type crystal oscillator will be required. Such a reference signal oscillation circuit is expensive, which makes this technique difficult to apply to household appliances.
A technique to address the above-described problems associated with the local oscillation circuit in the converter has conventionally been disclosed in Japanese Patent Laying-Open No. 10-200333.
Specifically, this technique utilizes, as an oscillation element, a transistor that operates in a microwave band. A circuit disclosed therein includes a microwave line connected to a base terminal of the transistor, and a dielectric resonator configured to couple with this microwave line. The microwave line has a length equal to xc2xd the wavelength of an oscillation frequency and its end is open-circuited. Alternatively, the microwave line may have a length equal to xc2xc the wavelength or an odd number of times thereof and its end is short-circuited. The resonance frequency of the dielectric resonator is set equal to the oscillation frequency.
This reference, however, has not disclosed any specific arrangements for interconnecting a plurality of patterns or any specific configurations for achieving stable oscillation. Thus, an attempt to realize a compact oscillation circuit for practical use according to this technique has encountered a number of obstacles.
An object of the present invention is to provide a dielectric resonance oscillation circuit that facilitates configuration of a feedback type oscillation circuit.
Another object of the present invention is to provide a dielectric resonance oscillation circuit that increases the degree of freedom in pattern designing.
A further object of the present invention is to provide a dielectric resonance oscillation circuit that makes a stable oscillation output obtainable.
A still further object of the present invention is to provide a dielectric resonance oscillation circuit that exhibits an increased degree of coupling with a dielectric resonator.
Yet another object of the present invention is to provide a dielectric resonance oscillation circuit that facilitates supply of power.
A further object of the present invention is to provide a dielectric resonance oscillation circuit that decreases a leakage level of an oscillation signal.
A still further object of the present invention is to provide a dielectric resonance oscillation circuit that facilitates taking of an output signal.
Yet another object of the present invention is to provide a dielectric resonance oscillation circuit that prevents a DC component from appearing at an outputting terminal.
A further object of the present invention is to provide a dielectric resonance oscillation circuit that decreases an effect of a circuit connected to the outputting terminal being posed on oscillation.
The dielectric resonance oscillation circuit according to an aspect of the present invention includes: a microstrip line connected to a signal input terminal of a transistor; a microstrip line connected to a signal output terminal of the transistor; and a dielectric resonator coupled with the microstrip lines at high frequency. Each of the microstrip lines is provided with a pattern that is branched off from the relevant microstrip line at an arbitrary angle.
Accordingly, it is readily possible to realize an arrangement in which the microstrip line connected to the signal output terminal is coupled to the dielectric resonator at high frequency and, at the same time, the dielectric resonator is coupled to the microstrip line connected to the signal input terminal at high frequency. In other words, a feedback path via the dielectric resonator can readily be configured.
Preferably, the pattern branched off from the microstrip line is provided with another pattern that is branched off from that pattern at an arbitrary angle.
Accordingly, the resulting angle between the pattern branched off from the microstrip line and the pattern branched off from that pattern can be set to any angle according to the design requirement.
Preferably, the microstrip line connected to the signal input terminal of the transistor and the microstrip line connected to the signal output terminal of the transistor each have its end open-circuited. The microstrip lines are both coupled to the dielectric resonator at high frequency.
Accordingly, a feedback path is formed through which a signal output from the signal output terminal of the transistor is guided via the dielectric resonator to the signal input terminal of the transistor. Thus, the transistor operates as a feedback type oscillation circuit.
Preferably, the microstrip line has a shape curved corresponding to the shape of the dielectric resonator.
Thus, by making the shape of the microstrip line correspond to that of the dielectric resonator, it is possible to increase the degree of coupling between the microstrip line and the dielectric resonator at high frequency.
Preferably, a direct current is supplied at an end of the pattern branched off from the microstrip line.
This pattern branched off from the microstrip line serves to prevent the DC supplying circuit from affecting the microstrip line.
Preferably, a stub is provided at an end of the branched pattern, which hinders passage of the oscillation signal.
Accordingly, leakage of the oscillation signal to the DC supplying circuit is prevented.
Preferably, the dielectric resonance oscillation circuit has a pattern that is branched off from the microstrip line in the vicinity of a connect point between the microstrip line and the signal output terminal of the transistor. The oscillation signal is taken out from an outputting end of the branched pattern that corresponds to its end opposite to the branched end.
Accordingly, the pattern branched off from the microstrip line prevents a load connected to the outputting end from affecting the connect point between the microstrip line and the signal output terminal.
Preferably, a capacitor is connected between the outputting end and the oscillation signal output terminal.
This capacitor hinders passage of a DC component.
Preferably, an attenuator is provided between the outputting end and the oscillation signal output terminal.
This attenuator serves to decrease an effect of a load connected to the oscillation signal output terminal being posed on the outputting end.